1. Field of the Invention
The present invention relates to a protection IC and a method of monitoring a battery voltage.
2. Description of the Related Art
In recent years, a lithium ion battery, which is one of secondary batteries, is being installed in a mobile device such as a digital camera. The lithium ion battery is vulnerable to an overcharge and an overdischarge. Therefore, it is necessary to provide a protection circuit, for example a protection integrated circuit (IC), in the lithium ion battery.
In a case where a plurality of cells of the lithium ion battery are connected in series and used, a disconnection between the cells and the protection IC needs to be avoided in order to properly detect an overcharge voltage of the cells of the lithium ion battery. If there is a disconnection, an accurate detection of the overcharge voltage is not performed, which may require a control such as prohibition of charge.
Japanese Laid-open Patent Publication No. 2009-95222 proposes that a detection current greater than a consumption current, which flows through various voltage monitoring circuits under a normal state, is flown through connection lines between cells and the voltage monitoring circuits when a disconnection is detected, a path through which a detection current flows is changed by a diode so that a corresponding potential relation between connection lines on positive and negative sides is changed when the disconnection occurs, and an inversion detection circuit detects the inversion of the potential relation, and a disconnection detection signal is output.
Japanese Laid-open Patent Publication No. 2012-98238 discloses a technique that a disconnection in a connecting portion between an electrode terminal of a battery pack and a power source terminal of a battery voltage monitoring circuit is detected.